1922 Encyclopædia Britannica/Optophone
OPTOPHONE. The optophone is an instrument for enabling totally blind people to read ordinary letterpress, such as a printed book or newspaper, without the necessity of printing it in raised type to be read by touch. The instrument was invented in 1914 by Dr. E. E. Fournier d'Albe, then a lecturer in physics in the university of Birmingham. It is based upon the properties of selenium, an element which is a better electrical conductor in light than in darkness. A beam of light is rendered intermittent by the interposition of a revolving siren disc and is then concentrated into a small bright point on the paper to be read. If the point on the paper is white, it will reflect the light; if it is black it will not. A selenium cell placed close to the paper, on receiving the reflected beam of intermittent light, will respond to each flash by a change in conductivity, and if the frequency of the flashes is of the “musical” order (between 30 and 30,000 flashes per second), a telephone receiver connected with the selenium and a battery will sound a musical note. A blind person could thus tell whether the paper is black or white.
That is the principle of the optophone. In practice a small row of luminous points is substituted for a single point, and each point in the row is given a different frequency by suitably perforating the siren disc. The row, usually of five or six points, just fills up the size of the tall letters of the print to be read. When the whole row falls upon the black stem of a letter there is silence in the telephone. As the letters pass their various shapes are indicated by the sounding or silence of the different notes, and after some practice the blind person learns to recognize letters from their sounds, and so to read ordinary type.
The first reading test was given by the inventor in March 1917, the matter read being a leading article in The Times. In Aug. 1918, Miss Mary Jameson, a blind pupil from Norwood, gave the first public reading demonstrations, reading an unknown page from a book at a speed of about two words per minute. Later, with an improved instrument, she attained a speed of about 20 words per minute. A new type of optophone was brought out in 1920 by Barr & Stroud, of Glasgow. In this instrument two selenium cells were used, balanced against each other in such a manner that white paper produced silence, and the black letters themselves made the musical sounds. Reading demonstrations were also given with this instrument, but any advantage in the way of ease of reading was found to be counter-balanced by a greater delicacy and complexity of adjustment. The new type is known as the “black-sounder,” and the original type is termed the “white-sounder.” The latter type was approved by the Inventions and Research Committee of the National Institute for the Blind in 1921 after an exhaustive series of tests. The optophone is intended to place the world's printed literature once more within reach of the blind. It is applicable, without special preparation, to any language, and can also be used for reading typescript, but not handwriting.
“The Optophone,” Journal of Roy. Soc. of Arts (1921); “TheOptophone,” St. Dunstan's Review, No. 55 (1921).
- (E. E. F. D'A.)